1. Field of the Invention
The present invention relates to an electrostatic motor driven by electrostatic force.
2. Description of the Related Art
An electrostatic motor includes a stator electrode member and a slider electrode member, which are provided with drive electrode patterns comprised of a plurality of conductors arranged at a fine pitch. An electrostatic motor is driven by applying cyclic voltage to these drive electrode patterns and utilizing the electrostatic attraction force between different polar electrodes and the electrostatic repulsion force between same polar electrodes between the stator electrode member and the slider electrode member, thereby causing the slider electrode member to slide relative to the stator electrode member.
Such an electrostatic motor includes a linear type and a rotary type. In a linear electrostatic motor, the slider electrode member is made to relatively slide linearly with respect to the stator electrode member. On the other hand, in a rotary electrostatic motor, the slider electrode member is made to rotate relatively with respect to the stator electrode member. In each type, the stator electrode member and the slider electrode member are arranged to face each other across a fine clearance in order to make the electrostatic motor work effectively and, at the same time, bead-shaped spherical members or cylindrical members having very small diameters are interposed between the two electrode members in order to reduce resistance due to mechanical friction between the two electrode members.
Further, in order to put the electrostatic motor to practical use, it is necessary to provide a high electric field. However, if there is gas present between the drive electrode patterns of the stator electrode member and the drive electrode patterns of the slider electrode member, a corona discharge etc. will be generated, so it will become difficult to maintain the insulation. Accordingly, the space between the drive electrode patterns of the stator electrode member and the drive electrode patterns of the slider electrode member had to be filled with an insulating liquid or made a vacuum (“Development of an Electrostatic Actuator Exceeding 10N Propulsive Force”, IEEE MEMS′ 92, Travemunde (Germany), Feb. 4-7, 1992, Toshiki NIINO et al).
FIG. 12 is a sectional view of a conventional electrode member 1 constituting a stator electrode member 1a or a slider electrode member 1b. The stator electrode member 1a and the slider electrode member 1b are configured substantially the same. At the time of production of the electrode member 1, a conductor such as a copper foil is attached by a binder to a base film 3 formed by an insulator (plastic film) and then etched etc. to form drive electrode patterns 2 on the base film 3. Next, the two surfaces of the base film 3 are covered by cover films 4 of an insulator (plastic films) to form insulating layers. Further, holes for connecting a power supply to the drive electrode patterns are formed in the electrode member 1.
FIGS. 13A to 13D are views for illustrating a conventional linear electrostatic motor. FIG. 13A is a perspective view of an electrode member 1 forming part of the linear electrostatic motor. One surface of the electrode member 1 is formed with drive electrode patterns 2 including three phase electrodes. In the drive electrode patterns 2, power supply holes for the different phases and the phase electrodes for the different phases are connected by conduction passages. Note that in order to avoid the conduction passages for the different phases intersecting with the electrodes etc. for other phases, the conduction passage for one phase electrode among the three phases is provided on the other surface of the electrode member 1. Further, the cover films 4 are attached by a binder to both surfaces of the electrode member 1 so as to cover the electrodes and conduction passages and form insulation layers. Note that FIGS. 13A to 13C show the cover films 4 as transparent members for the purpose of the explanation.
FIG. 13B shows a state where beads 10 are scattered on the electrode member 1 in order to maintain a clearance between the stator electrode member 1a and the slider electrode member 1b. Further, FIG. 13C shows an electrostatic motor built up of a set of a stator electrode member 1a and a slider electrode member 1b arranged parallel to each other. The stator electrode member 1a and the slider electrode member 1b are arranged so that the surfaces of the electrode members 1a and 1b provided with the drive electrode patterns 2 face each other. Further, FIG. 13D is a sectional view of the electrostatic motor built up of the set of the stator electrode member 1a and the slider electrode member 1b. The beads 10 are introduced together with an insulating liquid etc. into the clearance between the stator electrode member 1a and the slider electrode member 1b from one end of the clearance between the stator electrode member 1a and the slider electrode member 1b and flow out of the other end of the clearance and therefore flow through the clearance between the stator electrode member 1a and the slider electrode member 1b together with the insulating liquid. These beads 10 enable the clearance between the stator electrode member 1a and the slider electrode member 1b to be held.
The beads or cylindrical members used for holding the clearance between the stator electrode member and the slider electrode member and reducing the frictional resistance are not fixed, but are located in the clearance between the stator electrode member and the slider electrode member in a free state. Accordingly, when an insulating liquid is used as a medium for filling the clearance, the beads or cylindrical members are discharged from the clearance together with the insulating liquid, so the beads etc. must be mixed into the insulating liquid and introduced into the clearance between the two electrode members again. However, the clearance between the stator electrode member and the slider electrode member is a very narrow clearance of about tens of micrometers, therefore, it is difficult to make the beads etc. enter into this clearance again. For this reason, the beads etc. present in this clearance are decreased and, as a result, the stator electrode member and the slider electrode member directly contact each other to increase the frictional resistance between the electrode members. Further, over the long term, the stator electrode member and the slider electrode member are damaged by the friction resulting in electrical leakage, short-circuits and thereby reducing the service life.